Laser diode arrays with replaceable laser diode bars and methods of removing and replacing laser diode bars

ABSTRACT

The laser diode arrays with removable linear laser diode bars and the methods of removing and replacing linear laser diode bars of the present invention provide easy and immediate removal of individual linear laser diode bars in laser diode arrays. The laser diode array is at least partially made of a plurality of removable linear laser diode bars and a plurality of spacers, such that each removable linear laser diode bar is disposed between a respective pair of spacers. A linear laser diode bar may be slideably removed from between the respective pair of spacers in the laser diode array without breaking any mechanical connection between the removable linear laser diode bar and the respective pair of spacers. A replacement linear laser diode bar may then be slideably inserted between the respective pair of spacers without forming a mechanical connection between the replacement linear laser diode bar and the spacers.

BACKGROUND OF THE INVENTION

This invention is related to semiconductor laser devices and, moreparticularly to semiconductor laser devices with replaceable laser diodebars.

A number of lasers, such as slab and rod lasers, are designed to produceoutput pulses having a high average output power, such as 1,000 W-10,000W, operating either continuously or in a repetitively pulsed mode. Highlevels of output power are required in a number of applicationsincluding laser radar, mine detection, welding, material processing,surface coating, isotope separation and x-ray lithography, among others.In order to obtain such high power levels, a primary laser, such as aslab or a rod laser, can be pumped by a laser pump source, such as anarray of semiconductor laser diodes. The laser pump source must alsooperate at relatively high power levels and either at relatively highpulse repetition rates or continuously in order to generate thenecessary power to excite the primary laser.

Semiconductor lasers that pump a primary laser are typically made ofmultiple linear arrays of laser diodes, also known as linear laser diodebars. The linear laser diode bars are then arranged in a two-dimensionallaser diode array. To form the two-dimensional laser diode array, thelinear laser diode bars are typically soldered on microchannel heatsinks, which are subsequently stacked. The two-dimensional laser diodearray is capable of generating high intensity light for pumping theprimary laser.

Although the soldered two-dimensional laser diode array design issuitable for laser applications, it creates significant difficulty whenindividual linear laser diode bars must be replaced. The linear laserdiode bars occasionally fail for a variety of reasons, such as faceterosion (also called “spewing”), solder bonding failure, overheating,dark line defect growth, and gradual degradation, and must be replaced.Because the linear laser diode bars are soldered on heat sinks, however,the bars cannot be easily removed and reinserted. Instead, the entiretwo-dimensional laser diode array must either be scrapped or, if arepair is to be attempted, the entire array typically must bedisassembled by breaking the solder joints, if possible, replacing thefailed bar, and reassembling the array by resoldering the new laserdiode bar into position, then resoldering the array together. Because ofthe difficulty involved in breaking the solder joints and resolderingthe array, the replacement of conventional linear laser diode barscannot be performed by a typical user of a semiconductor laser device.In fact, the replacement process typically cannot even occur at or nearthe location at which the semiconductor laser device is deployed.Instead, the semiconductor laser device should be returned to itsmanufacturer or a maintenance depot for repair, which can take weeks.Thus, the semiconductor laser device is inoperable and unavailableduring the time it is being repaired and during the time it is intransit to and from the manufacturer.

Replacing a linear laser diode bar in a two-dimensional laser diodearray, therefore, can be costly to users of the semiconductor laserdevices who must be without the device for weeks while it is beingrepaired. In addition, it is costly and labor-intensive for themanufacturers of such semiconductor laser devices or for othermaintenance personnel to make the repairs necessary when a linear laserdiode bar must be replaced. As such, there is a need in the industry toprovide a two-dimensional laser diode array for use in semiconductorlaser devices, in which the individual linear laser diode bars may beeasily and immediately replaced without having to disassemble the entirearray and without a significant investment of time and/or money.

Thermal heat dissipation is another concern for semiconductor lasers. Inthis regard, in generating pulses having a relatively high averageoutput power and a relatively high repetition rate, the laser pumpsource generates a significant amount of heat, which elevates thetemperature of the laser pump source in the absence of external cooling.For example, the heat generated by a laser can be approximated by thedifference between the power input to the laser and the output powerreceived from the laser. Typically, the heat generated by a conventionallaser pump source is approximately 45%-60% of the input power, with theoverall efficiency of a solid state laser comprised of a laser pumpsource and a downstream laser system being about 10%-20%.

Lasers, such as semiconductor laser diode arrays, however, typicallyhave a maximum operating temperature above which the operation of thelaser can be unreliable. In addition, operation of a laser, such as asemiconductor laser diode array, at an elevated temperature generallyreduces the effective lifetime of the laser even though suchtemperatures may be below the maximum operating temperature. Forexample, operation of a semiconductor laser diode array at an elevatedtemperature can damage the emitting facet of the laser diode array,thereby impairing its performance.

One type of semiconductor laser diode array that provides suitablecooling during laser operation, while also being economical to producecompared to other semiconductor laser diode arrays, is the immersioncooled array. An immersion cooled array is made from linear laser diodebars mounted on microchannel coolers. The simple linear laser diode barsare capable of continuous wave (CW) or high duty factor operation byclamping the bars to liquid cooled heat sinks, and immersing the entiretwo-dimensional laser diode array in a flowing dielectric coolant.Details of the immersion cooled array are included in U.S. Pat. No.5,495,490, which is incorporated herein by reference.

Because of the time and expense involved in replacing individual linearlaser diode bars in conventional laser diode arrays, it would beadvantageous to be able to quickly and easily replace individual linearlaser diode bars in laser diode arrays. In particular, there is a needin the industry to utilize two-dimensional laser diode arrays, such asimmersion cooled arrays, in semiconductor laser diode devices, in whichthe arrays include individual linear laser diode bars that are easilyand immediately replaceable without a significant investment of timeand/or money. Furthermore, due to the efficient and economical nature ofthe immersion cooled array, it would be desirable to be able to utilizesuch an immersion cooled two-dimensional laser diode array made fromremovable linear laser diode bars in a variety of applications.

BRIEF SUMMARY OF THE INVENTION

The laser diode arrays with removable linear laser diode bars and themethods of removing and replacing linear laser diode bars of the presentinvention provide easy and immediate removal of individual linear laserdiode bars in laser diode arrays. Therefore, the individual linear laserdiode bars may be removed and replaced in the field without having totransport the laser diode array to a maintenance depot or the like,which significantly reduces the time and labor involved in the removaland replacement, as compared to conventional removal and replacementtechniques. In addition, the removable linear laser diode bars may beutilized with various types of laser diode arrays, including efficientand economical immersion cooled laser diode arrays.

One embodiment of the method for removing at least one of a plurality ofremovable linear laser diode bars from a laser diode array includesaccessing a removable linear laser diode bar within the laser diodearray and slideably removing the removable linear laser diode bar, suchas upon failure of the linear laser diode bar. The laser diode array isat least partially made of the plurality of removable linear laser diodebars and a plurality of spacers, such that each removable linear laserdiode bar is disposed between a respective pair of spacers. As such,when the removable linear laser diode bar is slideably removed from thelaser diode array, it is slideably removed from between the respectivepair of spacers in the laser diode array. In addition, the removablelinear laser diode bar is slideably removed without breaking anymechanical connection between the removable linear laser diode bar andthe respective pair of spacers.

To slideably remove the removable linear laser diode bar from betweenthe respective pair of spacers, a force may be applied to the removablelinear laser diode bar in a direction away from the plurality ofspacers. The force, therefore, overcomes the frictional force betweenthe removable linear laser diode bar and the respective pair of spacers.

The laser diode array may be immersion cooled. The immersion cooledlaser diode array includes a plurality of removable linear laser diodebars, a plurality of spacers, and a liquid coolant flowing about andthrough the immersion cooled laser diode array. As before, eachremovable linear laser diode bar is disposed between a pair of spacers.Replacing a removable linear laser diode bar includes at least partiallydraining the liquid coolant from the immersion cooled laser diode array.The removable linear laser diode bar is then accessed, which may involveopening a housing in which the removable linear laser diode bars aredisposed. The removable linear laser diode bar is slideably removed frombetween the respective pair of spacers in the array, and a replacementlinear laser diode bar is slideably inserted between the respective pairof spacers.

Slideably removing the respective removable linear laser diode bar mayinvolve removing the bar without breaking a mechanical connectionbetween the respective removable linear laser diode bar and therespective pair of spacers. Likewise, slideably inserting thereplacement linear laser diode bar may involve positioning thereplacement linear laser diode bar between the respective pair ofspacers without forming a mechanical connection between the replacementlinear laser diode bar and the respective pair of spacers. For example,in one embodiment of the present invention, the replacement linear laserdiode bar is secured between the respective pair of spacers withfrictional forces. After slideably inserting the replacement linearlaser diode bar, a liquid coolant may be introduced about and throughthe laser diode array for immersion cooling.

In addition to the methods for removing and replacing linear laser diodebars in laser diode arrays, another aspect of the present invention alsoincludes a laser diode assembly with such removable linear laser diodebars. The laser diode assembly comprises a two-dimensional laser diodearray that includes a plurality of linear laser diode arrays, each ofwhich has first and second major surfaces. First and second electrodesare electrically connected to the two-dimensional laser diode array forsupplying the array with electrical energy, such that at least one ofthe linear laser diode arrays is capable of emitting a laser output fromits emitting facet. At least one heat sink of a plurality of heatsinksis in thermal communication with each linear laser diode array to form aplurality of removable linear laser diode bars. The laser diode assemblyalso includes a plurality of spacers in a predetermined spaced apartrelationship with one another. As such, each removable linear laserdiode bar is slideably insertable and sideably removable between arespective pair of spacers. For instance, in one embodiment of the laserdiode assembly of the present invention, the removable linear laserdiode bar may be secured between the respective pair of spacers withfrictional forces.

The spacers may extend from a first end rearwardly to a second end andthe laser diode assembly may also include an electrically insulatingelement to which the second end of each spacer is fixed in order toelectrically isolate the spacers. In other embodiments, a plurality ofelectrically insulating sheets may be disposed between respective pairsof spacers to electrically isolate the spacers.

The two-dimensional laser diode array, the first and second electrodes,the plurality of heat sinks, and the plurality of spacers may bedisposed in a housing. A window may be located in the front surface ofthe housing, such that the respective emitting facets of the pluralityof linear laser diode arrays are positioned adjacent the window. In thisembodiment of the laser diode assembly of the present invention, thelaser diode array may be immersion cooled by positioning the pluralityof linear laser diode arrays adjacent the window in a predeterminedspaced apart relationship such that liquid coolant flows between thewindow and the linear laser diode arrays. The housing also may defineinlet and outlet ports through which the liquid coolant flows into andout of the housing.

The heat sinks may extend rearwardly from the plurality of linear laserdiode arrays, and first channels may be defined between the rearwardlyextending heat sinks. The first channels can, therefore, receive theliquid coolant such that the liquid coolant directly contacts and coolsthe linear laser diode arrays by immersion while maintaining electricalisolation between the first and second electrodes. The first channelsmay be further defined by disposing a first end of each heat sink on oneof the first and second major surfaces of a linear laser diode array.Each heat sink may extend rearwardly to a second end, and electricallyinsulating members may be disposed between the respective second ends ofa pair of heat sinks of each removable linear laser diode bar, whichfurther defines the first channels between the pair of heat sinks, theelectrically insulating members and the linear laser diode arrays.

Additionally, second channels may be defined between the removablelinear laser diode bars that extend forwardly from the plurality ofelectrically isolated spacers, when the removable linear laser diodebars are inserted between respective pairs of spacers. The secondchannels can also receive liquid coolant such that the liquid coolantdirectly contacts and cools the removable linear laser diode bars byimmersion while maintaining electrical isolation between the first andsecond electrodes.

In a further embodiment of the laser diode assembly of the presentinvention, the two-dimensional laser diode array, the first and secondelectrodes, the heat sinks, and the spacers are disposed in the housing,and a solid state laser is disposed in an opening in the front surfaceof the housing. Thus, the two-dimensional laser diode array is disposedwithin the housing such that the respective emitting facets of the laserdiode arrays are positioned adjacent the solid state laser in apredetermined spaced apart and aligned relationship, such that the laserdiode array pumps the solid state laser. The laser diode array of thisembodiment may be immersion cooled by positioning the linear laser diodearrays adjacent the solid state laser such that liquid coolant flowsbetween the solid state laser and the linear laser diode arrays, whichcools both the solid state laser and the linear laser diode arrays.

The laser diode assembly with removable linear laser diode bars and themethods of removing and replacing linear laser diode bars of the presentinvention provide easy and immediate removal of individual linear laserdiode bars in laser diode arrays. As such, the cost and labor involvedin removing and replacing individual linear laser diode bars issignificantly reduced, as compared to conventional techniques. Inaddition, the laser diode assembly of the present invention functions atleast as well and at least as efficiently as conventional laser diodearrays, particularly in instances in which the laser diode assembly ofthe present invention is immersion cooled.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a block diagram of a laser system according to one embodimentof the present invention, that illustrates the relationship of a laserpump source, a primary laser and a Q-switch;

FIG. 2 is a perspective view of a semiconductor laser diode assemblywith removable linear laser diode bars, according to one embodiment ofthe present invention; and

FIG. 3 is a perspective view of a semiconductor laser diode deviceaccording to one embodiment of the present invention, with portions ofthe housing and window removed to illustrate the internal componentsthereof.

DETAILED DESCRIPTION OF THE INVENTION

The present inventions now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

Referring now to FIG. 1, a laser system 10 which is adapted to provide alaser output having a relatively high output power level is illustratedin block diagram form. In particular, the laser system includes a laserpump source 12 for emitting laser output pulses. The output pulses arepreferably produced at a relatively high repetition rate and have arelatively high average power level. For example, the laser pump sourcecan be a two-dimensional laser diode array, which produces pulses havingan average power level of 100-1000 W/cm² at an average repetition rateof 100-1000 Hz.

The output pulses emitted by the laser pump source 12 may be applied toa primary laser 14, such as a slab or rod laser. For example, theprimary laser can be a Nd:YAG slab laser. The output of the primarylaser can, in turn, be controlled by a Q-switch 16. As known to thoseskilled in the art, the Q-switch induces the primary laser to emit shortpulses with high peak power as shown in FIG. 1. Alternatively, inembodiments in which the laser system 10 does not include a Q-switch,the primary laser will generally operate in either a continuous wave(CW) or a long pulse mode. If included, the Q-switch defines, at leastin part, the primary laser cavity 11 and controls the output of theprimary laser such that only output pulses having a power level above apredetermined threshold level are generated. For example, a Q-switchedNd:YAG laser generally produces output pulses having an average powerlevel of 10 W to more than 1000 W at an average pulse repetition rate of1000 Hz or greater.

According to the present invention, the laser pump source 12 is asemiconductor laser assembly including a semiconductor laser device 18.In one preferred embodiment, the semiconductor laser device includes aplurality of linear laser diode arrays 19 configured as atwo-dimensional laser diode array. For example, one embodiment of thesemiconductor laser device of the present invention includes atwo-dimensional laser diode array, and is illustrated in FIGS. 2 and 3.As known to those skilled in the art, the individual laser diodes oremitters 20 of the semiconductor laser device are preferablyelectrically connected such that the output of the laser diode array issynchronized. In addition, it will be apparent to one skilled in the artthat the lines of FIGS. 2 and 3 that separate the individual emittersare for purposes of illustration and form no material portion of theknown laser diode array.

The plurality of linear laser diode arrays 19 that comprise thesemiconductor laser device 18 can be fabricated of any of thesemiconducting materials known to those skilled in the art. For example,the plurality of linear laser diodes can be comprised of AlGaAs, InGaAs,or GaInAsP. The plurality of linear laser diodes can be comprised ofother materials known to those skilled in the art, however, withoutdeparting from the spirit and scope of the present invention. Inaddition, each linear laser diode array can include a plurality ofindividual emitters 20, such as between sixteen and thirty emitters inone exemplary embodiment.

As further illustrated in FIGS. 2 and 3, the semiconductor laser device18 can also include a plurality of heat sinks 30. Typically, the heatsinks are comprised of a material having relatively high thermalconductivity. In addition, the heat sinks are preferably electricallyconductive so as to electrically connect the plurality of linear laserdiode arrays 19. Thus, the plurality of heat sinks can be comprised ofcopper or copper alloys, gold, silver or other known materials that areboth electrically and thermally conductive.

A heat sink is preferably in thermal communication with each linearlaser diode array. In this regard, each linear laser diode arraypreferably has first and second opposed major surfaces 22 and 24,respectively. As shown in FIGS. 2 and 3, a heat sink 30 may be disposedon each first and second major surface 22 and 24 to create a pluralityof removable linear laser diode bars 31. One embodiment of removablelinear laser diode bars 31 is shown in FIG. 2. To form a linear laserdiode bar, a linear laser diode array 19 may be soldered between a pairof heat sinks 30. In other embodiments of the linear laser diode bars31, any type of anode and cathode surfaces known to those skilled in theart, and having an appropriate thickness, may be disposed on each firstand second major surface 22 and 24 of the linear laser diode arrays 19.The heat sinks disposed on the first and second major surfaces 22 and 24may be the same size and shape, and may be made of the same thermallyand electrically conductive material. Alternatively, at least one of theheat sinks 30 disposed on one of the first and second major surfaces 22and 24 of the linear laser diode arrays 19 may have a different size,shape, and/or made of a different thermally and electrically conductivematerial than the heat sink disposed on the other of the first andsecond major surfaces. The plurality of heat sinks 30 also electricallyconnect each of the plurality of linear laser diode arrays 19. Theplurality of heat sinks may extend rearwardly from the two-dimensionallaser diode array to define a plurality of first channels 32 betweeneach pair of rearwardly extending heat sinks and the linear laser diodearray 19 disposed between the pair of heat sinks. In the embodimentillustrated in FIG. 2, each heat sink extends from a first end 34disposed on a linear laser diode array rearwardly to an opposed secondend 36.

In some embodiments of the semiconductor laser device 18 of the presentinvention, a plurality of electrically insulating members 38 mayelectrically isolate each pair of heat sinks 30 disposed on the linearlaser diode arrays 19. The plurality of electrically insulating members38 are typically comprised of an insulating material, such as BerylliumOxide (BeO), a dielectric and/or a plastic material. At least one membermay be disposed between the respective second ends 36 of each pair ofheat sinks 30 to further define a first channel 32. In particular, eachfirst channel of this embodiment may be defined between a pair of heatsinks, an electrically insulating member disposed between the pair ofheat sinks and a linear laser diode array 19 also disposed between thepair of heat sinks.

A plurality of spacers 37 may also be included in the semiconductorlaser device 18 of the present invention. The spacers 37, like the heatsinks 30, may be comprised of a material having relatively high thermalconductivity. In addition, the spacers 37 are preferably electricallyconductive so as to electrically connect the plurality of linear laserdiode bars 31. Thus, the plurality of spacers can be comprised of copperor copper alloys, gold, silver or other known materials that are bothelectrically and thermally conductive.

The spacers 37 are positioned in a predetermined spaced apartrelationship with one another, such that each removable linear laserdiode bar 31, formed of a combination of a linear laser diode array,sandwiched between a pair of heat sinks in one embodiment, is slideablyinsertable and slideably removable between a respective pair of spacers.In a preferred embodiment of the present invention, the spacers 37 aremounted to and extended outwardly from an electrically insulatingelement 39, typically comprised of an insulating material, such asBeryllium Oxide (BeO), a dielectric and/or a plastic material, toelectrically isolate the spacers. The spacers 37 may extend from a firstend 41 to a second end 43, such that the second end of each spacer isfixed to the electrically insulating element 39. The spacers 37 may bemounted to the electrically insulating element 39 in any manner known tothose skilled in the art. For instance, the spacers 37 may be mounted tothe electrically insulating element 39 by casting the second end of thespacers within a dielectric block that forms the electrically insulatingelement.

In other embodiments of the present invention, the spacers 37 areelectrically isolated by disposing a plurality of electricallyinsulating sheets between the respective pairs of spacers 37. Forexample, electrically insulating sheets may be disposed on each of themajor surfaces of the spacers 37, such that the sheets are locatedbetween the spacers and the heat sinks 30. The spacers may beelectrically isolated in any other manner known to those skilled in theart.

As stated above, the linear laser diode bars 31, typically incombination with the respective heat sinks, are slideably insertable andslideably removable between a respective pair of spacers. A linear laserdiode bar 31, therefore, may be removed from between the respective pairof spacers without breaking a mechanical connection between the linearlaser diode bar and the respective pair of spacers. As such, the linearlaser diode bars may be secured between the respective pairs of spacerswithout creating a mechanical connection between the linear laser diodebars and the respective pairs of spacers by any manner known to thoseskilled in the art. For instance, a linear laser diode bar 31 may beremovably secured between a respective pair of spacers with frictionalforces. In this embodiment, a force may be applied to the linear laserdiode bar in a direction away from the plurality of spacers, such as ina direction away from the electrically insulating element 39 in theembodiment of FIG. 2, in order to slideably remove a linear laser diodebar 31 from the laser diode array. The force applied to the linear laserdiode bar is, therefore, enough to overcome the frictional forcesecuring the linear laser diode bar between the respective pair ofspacers.

After removing a linear laser diode bar 31 from between a respectivepair of spacers, a replacement linear laser diode bar may be insertedbetween the respective pair of spacers. The linear laser diode bars maybe inserted and/or removed in any manner known to those skilled in theart. For instance, the linear laser diode bars may be inserted and/orremoved via manual means, such as by hand or with a manually controlledtool, or via electro-mechanical means, such as a mechanism that iscontrolled by electrical signals originating from a computer processor.

The laser diode assembly with removable linear laser diode bars 31 ofthe present invention, therefore, permits easy and immediate removal andreplacement of individual linear laser diode bars. As such, the cost andlabor involved in removing and replacing individual linear laser diodebars is significantly reduced as compared to conventional techniques. Bysimplifying the replacement procedure, at least some repairs mayadvantageously be performed in the field, thereby avoiding having toship the laser array assembly to a maintenance depot and incurring thedelays associated therewith. In addition, the laser diode assembly ofthe present invention function at least as well and at least asefficiently as conventional laser diode arrays.

As also illustrated in FIG. 3, the semiconductor laser device 18 of thepresent invention is electrically activated. Thus, the semiconductorlaser device preferably includes first and second electrodes,electrically connected to the semiconductor laser device, for supplyingelectrical energy to the semiconductor laser device. Upon sufficientelectrical actuation, the individual emitters 20 of the semiconductorlaser device emit a laser output through an emitting or front facet ofthe semiconductor laser device and, more particularly, through therespective emitting or front facets of the individual emitters 20.Typically, the laser output is a series of pulses having a relativelyhigh repetition rate, though CW operation may also be desirable. Thefirst and second electrodes may be separate components attached to thesemiconductor laser device to supply electrical energy to thesemiconductor laser device. Alternatively, the outermost spacers 37 mayserve as the first and second electrodes for receiving the electricalinput.

During the emission of the laser output, the semiconductor laser device18 generates heat, which increases the temperature of the semiconductorlaser device in the absence of cooling. In order to maintain thesemiconductor laser device at a temperature safely below a predeterminedmaximum operating temperature and, consequently, to prevent damage tothe laser device, the semiconductor laser device is cooled. In thisregard, the laser diode assembly of the present invention may be cooledin any manner known to those skilled in the art. In a preferredembodiment of the present invention, the laser diode assembly is cooledby immersion. A method and apparatus for immersion cooling of asemiconductor laser device is described in U.S. Pat. No. 5,495,490, thecontents of which are incorporated herein by reference.

In the immersion cooling embodiment of the present invention, liquidcoolant circulates about the electrically activated semiconductor laserdevice 18. More preferably, the liquid coolant flows about and directlycontacts the emitting facet of the semiconductor laser device. Theliquid coolant has a temperature less than the temperature of thesemiconductor laser device during the emission of the laser output.Accordingly, the circulation of liquid coolant about the semiconductorlaser device draws heat from and, consequently, cools the laser device.

The liquid coolant is preferably a dielectric liquid, which is bothelectrically and optically passive. Accordingly, the liquid coolant istransparent at the predetermined range of wavelengths at which thesemiconductor laser device 18 emits a laser output. In addition, theliquid coolant does not absorb the laser emissions within thepredetermined range of wavelengths such that the output power levelproduced by the semiconductor laser device is not attenuated ordiminished by the circulating liquid coolant. In one embodiment, thedielectric liquid coolant is a fluorinert compound, such as FC75 orFC77. In another embodiment, the dielectric liquid coolant is a lighthydrocarbon compound, such as hexane. In yet another embodiment, thedielectric liquid coolant is freon, anhydrous ammonia, a silicon-basedliquid, deionized water, or a water and glycol mixture.

By directly contacting the semiconductor laser device 18 and, moreparticularly, by directly contacting the emitting facet of thesemiconductor laser device, the thermal impedance of the semiconductorlaser assembly 12 is reduced. In addition, the direct contact of theliquid coolant with the individual emitters 20 of the linear laserdiodes of the semiconductor laser device provides for increased orenhanced cooling of the emitting facets such that the semiconductorlaser device can be operated at relatively high temperatures withoutdamaging the emitting facets of the linear laser diodes. Accordingly,the operating lifetime of the semiconductor laser device is prolonged.Further, the immersion of the semiconductor laser device and, inparticular, the immersion of the emitting facet of the semiconductorlaser device in the liquid coolant significantly reduces the risk thatthe emitting facet of the semiconductor laser device is exposed toexternal contamination.

In operation, liquid coolant flows through the plurality of firstchannels 32 defined by the rearwardly extending heat sinks 30 to contactand cool the plurality of linear laser diode arrays 19 by drawing heatfrom the heat sinks. Since the coolant is a dielectric liquid, however,the coolant maintains the electrical isolation between the first andsecond electrodes.

When more than one linear laser diode bar 31 is inserted betweenrespective pairs of spacers 30 in the laser diode array 18 of thepresent invention, the linear laser diode bars may advantageously extendforwardly from the spacers to define second channels 33 between theforwardly extending linear laser diode bars, as shown in FIG. 2. Inoperation, liquid coolant also may flow through the plurality of secondchannels 33 defined by the forwardly extending linear laser diode bars31 to further contact and cool the plurality of linear laser diodearrays 19 by drawing heat from the heat sinks.

The semiconductor laser assembly 12 of the present invention alsopreferably includes a housing 40 in which the semiconductor laser device18 is disposed. As shown in a partial fragmentary perspective view inFIG. 3, the housing has a front surface 42 defining an opening 44therein. The laser output of the semiconductor laser device ispreferably emitted through the opening defined in the first surface ofthe housing. According to a first embodiment, a window 46 is disposed inthe opening in the front surface of the housing. Preferably, the windowis comprised of material, which is transparent to the laser outputwithin the range of wavelengths which the semiconductor laser deviceemits. For example, the window can be comprised of glass, fused silicon,or sapphire. However, the window can be comprised of other materialswithout departing from the spirit and scope of the present invention.

The semiconductor laser device 18 is preferably disposed within thehousing 40 such that the emitting facet of the semiconductor laserdevice is positioned adjacent the window 46 in a predetermined spacedapart relationship. As shown in FIG. 3, liquid coolant circulatesbetween the window and the semiconductor laser device, through the heatsink 30, and, in addition, between the window and the individualemitters 20 of the linear laser diodes of the semiconductor laser deviceto thereby draw heat from and cool the semiconductor laser device.

In another embodiment, the primary laser 14, such as a solid statelaser, is disposed within the opening 44 defined in the front surface 42of the housing 40. As described above, the semiconductor laser device 18is disposed within the housing such that the emitting facet of the laserdevice is positioned adjacent to the solid state laser in a spaced apartand aligned relationship. Thus, the semiconductor laser device pumps thesolid state laser. In addition, the liquid coolant circulates betweenthe solid state laser and the semiconductor laser device to thereby drawheat from and cool both the solid state laser and the semiconductorlaser device.

As illustrated in FIG. 3, the housing 40 also preferably includes aninlet port 48 and an outlet port 50 through which the liquid coolantflows. As also illustrated schematically in FIG. 3, the semiconductorlaser assembly can include a heat exchange means, such as an externalcooler or chiller 52. For example, the external cooler can be a radiatoror other type of heat exchanger. In one embodiment, the external cooleris self-sustaining, that is, the external cooler supports fluid flow inonly one direction. The external cooler of this embodiment generallyincludes a series of valves, which only permit fluid flow in the onepredetermined direction.

In operation, the liquid coolant enters the semiconductor laser assembly12 through the inlet port 48 defined in the housing 40, flows through afirst channel 32 defined between a pair of adjacent heat sinks 30 and/ora second channel 33 defined between a pair of adjacent linear laserdiode bars 31 inserted between a respective pair of spacers 37, andexits from the housing through an outlet port 50 defined in an opposedsidewall of the housing. While circulating through the first and/orsecond channels, the liquid coolant absorbs heat or energy from thesemiconductor laser device 18 and the heat sinks 30, thereby cooling thesemiconductor laser device. By absorbing heat from the semiconductorlaser device, however, the temperature of the liquid coolant increases.Thus, upon exiting the housing through the outlet port, the liquidcoolant preferably flows through the radiator or heat exchanger. Withinthe heat exchanger, liquid coolant discharges at least a portion of theheat, which it absorbed from the semiconductor laser device such thatthe resulting temperature of the liquid coolant decreases.

The inlet and outlet ports 48 and 50 of the illustrated embodiment aredefined in the opposed sidewalls of the housing 40. However, the inletand outlet ports can, instead, be defined through other walls of thehousing without departing from the spirit and scope of the presentinvention. For example, in one embodiment, the semiconductor laserassembly 12 also includes coolant directing means for directing the flowof the liquid coolant in a direction perpendicular to the emitting facetof the semiconductor laser device 18. In this embodiment, theelectrically insulating members 38 define fluid passageways therethroughsuch that liquid coolant introduced through an inlet port defined in arear surface of the housing flows through the fluid passageway of arespective electrically insulating spacer and into a corresponding firstchannel 32 defined between adjacent heat sinks 30. By directing the flowof liquid coolant in a direction perpendicular to the emitting facet ofthe semiconductor laser device and, more particularly, perpendicular tothe emitting facets of the laterally extending linear laser diode array18, the temperature or energy level of the liquid coolant which contactseach individual emitter 20 of the linear array is the same, regardlessof the lateral position of the respective laser diode. Thus, eachindividual emitter can be cooled equally.

In addition, the heat transfer from the heat sinks 30 of thesemiconductor laser assembly 12 of the present invention to the liquidcoolant flowing thereby can be further modified by controlling the typeof coolant flow. For example, a highly turbulent or a relatively laminarsmooth coolant flow can be created through the first and/or secondchannels 32, 33. In addition, the heat transfer can be further modifiedby controlling the length of the channels, that is, the distance betweenthe rear surface of the linear laser diode array 19 and the electricallyinsulating spacers 38 for the first channel, or the distance between thespacers 37 and the front surface 42 of the housing. Thus, for a shortchannel, i.e., a channel having a length less than about 1-2 mm, inwhich liquid coolant circulates according to a laminar flow, the heattransfer depends more directly upon the thermal conductivity of theliquid coolant. However, for a long channel, i.e., a channel having alength greater than about 10 mm, in which liquid coolant circulatesaccording to a laminar flow, the heat transfer depends more directly onthe thickness of the heat sink and the thermal conductivity of the heatsink, and less directly upon the thermal conductivity of the liquidcoolant.

Alternatively, a turbulent flow can be created within the respectivechannels 32, 33. A turbulent flow creates a greater dependence of theheat transfer on the density and flow velocity of the liquid coolant,and less dependence on the thermal conductivity of the liquid coolant.Thus, relatively dense coolants, which circulate rapidly in a turbulentmanner will provide increased heat transfer.

According to the present invention, the direct contact of the liquidcoolant with the individual emitters 20 of the semiconductor laserdevice 18 more efficiently cools the semiconductor laser device. Themore efficient cooling is particularly effective for removing heat fromlaser diode pump arrays, which produce output pulses having a relativelyhigh average power and a relatively high repetition rate. In addition,the dielectric liquid coolant is preferably both electrically andoptically passive to maintain electrical isolation between theelectrodes, which supply electrical energy to the semiconductor laserdevice without absorbing the laser output emitted by the semiconductorlaser device.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

That which is claimed:
 1. A method for replacing at least one of aplurality of removable linear laser diode bars in an immersion cooledlaser diode array, comprising: providing the immersion cooled laserdiode array comprising a plurality of removable linear laser diode ban,a plurality of spaces, and a liquid coolant flowing about and throughthe immersion cooled laser diode array, and wherein each removablelinear laser diode bar is disposed between a pair of spacers; at leastpartially draining the liquid coolant from the immersion cooled laserdiode array; accessing a respective removable linear laser diode bar;slideably removing the respective removable linear laser diode bar frombetween the respective pair of spacers in the immersion cooled laserdiode array; maintaining a predetermined spaced apart relationshipbetween the respective pair of spacers to facilitate subsequentinsertion of a replacement linear laser diode bar; and slideablyinserting a replacement linear laser diode bar between the respectivepair of spacers.
 2. The method for replacing at least one removablelinear laser diode bar according to claim 1, further comprisingintroducing liquid coolant about and through the immersion cooled laserdiode array after slideably inserting the replacement linear laser diodebar.
 3. The method for replacing at least one removable linear laserdiode bar according to claim 1, wherein slideably inserting thereplacement linear laser diode bar comprises positioning the replacementlinear laser diode bar between the respective pair of spacers withoutforming a mechanical connection between the replacement linear laserdiode bar and the respective pair of spacers.
 4. The method forreplacing at least one removable linear laser diode bar according toclaim 1, wherein slideably inserting the replacement linear laser diodebar comprises securing the replacement linear laser diode bar betweenthe respective pair of spacers with frictional forces.
 5. The method forreplacing at least one removable linear laser diode bar according toclaim 1, wherein slideably removing the respective removable linearlaser diode bar comprises removing the respective removable linear laserdiode bar without breaking a mechanical connection between therespective removable linear laser diode bar and the respective pair ofspacers.
 6. The method for removing at least one removable linear laserdiode bar according to claim 1, wherein accessing the respectiveremovable linear laser diode bar comprises opening a housing in whichthe plurality of removable linear laser diode bars are disposed.
 7. Alaser diode assembly comprising: a two-dimensional laser diode arraycomprising a plurality of linear laser diode arrays, wherein each linearlaser diode array has first and second major surfaces; first and secondelectrodes, electrically connected to said two-dimensional laser diodearray, for supplying electrical energy thereto such data at least one ofthe plurality of linear laser diode arrays is capable of emitting alaser output from an emitting facet thereof; a plurality of heat sinksin thermal communication with respective ones of the plurality of linearlaser diode arrays to form a plurality of removable linear laser diodebars; a plurality of spacers in a predetermined spaced apartrelationship with one another such that each removable linear laserdiode bar is slideably insertable and slideably removable between arespective pair of spacers, wherein the respective pair of spacersmaintain the predetermined spaced apart relationship after removal ofthe removable linear laser diode bar to facilitate subsequent insertionof a replacement linear laser diode bar; and a liquid coolant flowingabout and through the laser diode assembly to form an immersion cooledlaser diode assembly.
 8. The laser diode assembly according to claim 7,wherein at least one removable linear laser diode bar is secured betweenthe respective pair of spacers with frictional forces to permit theremovable linear laser diode bar to be slideably insertable andslideably removable between the pair of spacers.
 9. The laser diodeassembly according to claim 7, wherein each spacer extends from a firstend rearwardly to a second end, and the laser diode array furthercomprising an electrically insulating element to which the second end ofeach spacer is fixed in order to electrically isolate the spacers. 10.The laser diode assembly according to claim 7, further comprising aplurality of electrically insulating sheets disposed between respectivepairs of the spacers in order to electrically isolate the spacers. 11.The laser diode assembly according to claim 7, further comprising: ahousing in which said two-dimensional laser diode array, said first andsecond electrodes, said plurality of heat sinks, and said plurality ofspacers are disposed, said housing having a front surface defining anopening therein; and a window disposed within the opening defined in thefront surface of the housing, said two-dimensional laser diode arraybeing disposed within said housing such that the respective emittingfacets of the plurality of linear laser diode arrays are positionedadjacent said window.
 12. The laser diode assembly according to claim11, wherein the plurality of linear laser diode arrays are positionedadjacent said window in a predetermined spaced apart relationship suchthat liquid coolant flows between said window and the plurality oflinear laser diode arrays to thereby cool the laser diode assembly byimmersion.
 13. The laser diode assembly according to claim 12, whereinsaid housing further defines an inlet port and an outlet port throughwhich liquid coolant flows.
 14. The laser diode assembly according toclaim 7, wherein said plurality of heat sinks extend rearwardly fromsaid plurality of linear laser diode arrays.
 15. The laser diodeassembly according to claim 14, wherein said plurality of heat sinksdefine a plurality of first channels between the rearwardly extendingheat sinks, the plurality of first channels being adapted to receiveliquid coolant such that the liquid coolant directly contacts and coolsthe plurality of linear laser diode arrays while maintaining electricalisolation between said first and second electrodes to form an immersioncooled laser diode assembly.
 16. The laser diode assembly according toclaim 15, wherein each heat sink extends from a first end disposed onone of the first and second major surfaces of a linear laser diode arrayrearwardly to a second end, the laser diode array further comprising aplurality of electrically insulating members, at least one of saidelectrically insulating members disposed between the respective secondends of the pair of heat sinks of each movable linear laser diode bar tofurther define a first channel.
 17. The laser diode assembly accordingto claim 7, wherein said plurality of spacers are electrically isolated,and wherein the plurality of removable linear laser diode bars extendforwardly from said plurality of spacers to define a plurality of secondchannels between the forwardly extending removable linear laser diodebars when the plurality of removable bars are inserted betweenrespective pairs of spacers, the plurality of second channels beingadapted to receive liquid coolant such that the liquid coolant directlycontacts and cools the plurality of removable linear laser diode barswhile maintaining electrical isolation between said first and secondelectrodes to form an immersion cooled laser diode assembly.
 18. Thelaser diode assembly according to claim 17, wherein the plurality oflinear laser diode arrays are positioned adjacent said solid state lasersuch that liquid coolant flows between said solid state laser and theplurality of linear laser diode arrays to thereby cool both said solidstate laser and the plurality of linear laser diode arrays by immersion.19. The laser diode assembly according to claim 7, further comprising: ahousing in which said two-dimensional laser diode array, said first andsecond electrodes, said plurality of heat sinks, and said plurality ofspacers are disposed, said housing having a front surface defining anopening therein; and a solid state laser disposed within the openingdefined in the front source of said housing, said two-dimensional laserdiode array being disposed within said housing such that the respectiveemitting facets of the plurality of linear laser diode arrays arepositioned adjacent said solid state laser in a predetermined spacedapart and aligned relationship such that the laser diode array pumpssaid solid state laser.